Powder coating compositions containing anhydride end-caped crystalline polyesters

Abstract

Thermosetting coating compositions containing amorphous and semi-crystalline polyesters are provided. They are useful in coating compositions, especially for low temperature powder coating applications.

1 . A thermosetting coating composition comprising a binder wherein 100 parts by weight of this binder comprises: 
 (A) 1 to 50 parts by weight of a carboxylic acid group containing amorphous polyester having an acid number of from 15 to 100 mg KOH/g.    (B) 1 to 50 parts by weight of a carboxylic acid group containing semi-crystalline polyester, said polyester comprising the reaction product of an anhydride of a polybasic organic carboxylic acid and a hydroxyl group containing semi-crystalline polyester.    (C) 1 to 90 parts by weight of a glycidyl group containing polyphenoxy resin having an epoxy equivalent weight of 150 to 1500 g/equiv.    (D) 0 to 85 parts by weight of a glycidyl group containing (meth) acrylate copolymer having an epoxy equivalent weight of 1.0 to 5.0 milli-equivalents of epoxy/gram of polymer.    (E) 0 to 20 parts by weight of a curing agent different from (C) and (D) and having functional groups reactable with the polyester (A) and (B) carboxylic acid groups.    
     
     
         2 . The composition according to  claim 1  wherein the carboxylic acid group containing amorphous polyester (A) is composed of from 50 to 100% mole of terephthalic acid or isophthalic acid or their mixtures and from 0 to 50% mole of an aliphatic, cycloaliphatic or aromatic polyacid different from terephthalic acid or isophthalic acid, referring to the polyacid constituents, and from 40 to 100% mole of neopentyl glycol and from 0 to 60% mole of another aliphatic and/or cycloaliphatic polyol referring to the polyol constituents.  
     
     
         3 . The composition according to  claim 1  wherein the carboxylic acid group containing semi-crystalline polyester (B) is obtained from the ring opening reaction of the anhydride group of trimellitic anhydride and/or pyromellitic anhydride with a hydroxyl group containing semi-crystalline polyester having a hydroxyl number of from 15 to 70 mg KOH/g, and comprising from 70 to 100% mole of terephthalic acid, 1, 4-cyclohexanedicarboxylic acid or a linear chain dicarboxylic acid containing 4 to 16 carbon atoms and from 0 to 30% mole of another aromatic, aliphatic or cycloaliphatic polyacid, referring to the polyacid constituents, and from 70 to 100% mole of a cycloaliphatic or linear chain aliphatic polyol containing 2 to 16 carbon atoms and from 0 to 30% mole of another aliphatic or cycloaliphatic polyol, referring to the polyol constituents.  
     
     
         4 . The composition according to  claim 1  wherein the glycidyl group containing polyphenoxy resin (C) is a Bisphenol A based epoxy resin or a phenol or cresol epoxy Novolac.  
     
     
         5 . The composition according to  claim 1  wherein the glycidyl group containing (meth)acrylate copolymer (D) is prepared from 10 to 90% mole of a glycidyl group containing monomer and from 90 to 10% mole of one or more monomer copolymerizable with the glycidyl group containing monomers, said (meth)acrylate copolymer having a number averaged molecular weight of from 1000 to 15000.  
     
     
         6 . The composition according to  claim 1  wherein the curing agent (E) is triglycidyl isocyanurate, diglycidyl terephthalate, triglycidyl trimellitate, or a mixture of them, or a β-hydroxyalkylamide group containing compound.  
     
     
         7 . The composition according to  claim 1  wherein the carboxylic acid group containing amorphous polyester (A) has the following properties: 
 a number averaged molecular weight of from 1 100 to 15000, a glass transition temperature (Tg) from 40 to 80° C. and an ICI (cone/plate) viscosity at 200° C. ranging from 5 to 15000 mPa.s.    
     
     
         8 . The composition according to  claim 7  wherein the carboxylic acid group containing amorphous polyester (A) has an acid number of from 30 to 70 mg KOH/g.  
     
     
         9 . The composition according to  claim 1  wherein the carboxylic acid group containing semi-crystalline polyester (B) has the following properties: 
 an acid number from 30 to 120 mg KOH/g,    a number average molecular weight ranging from 1 100 to 17000,    a fusion zone from 50 to 150° C.,    a glass transition temperature (Tg) below 40° C.,    a degree of crystallinity of at least 5 J/g, and    an ICI (cone/plate) viscosity at 100° C. of at least 10 mPa.s.    
     
     
         10 . The composition according to  claim 9  wherein the acid number of (B) is from 50 to 100 mg KOH/g.  
     
     
         11 . The composition according to  claim 1  wherein the glycidyl group containing acrylic copolymer (D) has the following properties: 
 a number average molecular weight ranging from 1000 to 15000,    a glass transition temperature (Tg) from 40 to 85° C., measured by Differential Scanning Calorimetry (DSC), according to ASTM D3418 with a heating gradient of 20° C. per minute, and    an ICI (cone/plate) viscosity determined by the ICI method at 200° C. of at least 100 mPa.s.    
     
     
         12 . The composition according to  claim 1  containing from 0.1 to 5.0 parts by weight, referring to 100 parts of binder, of a catalyzing compound selected from the group consisting of amine, phosphine, ammonium salt and phosphonium salt catalysts.  
     
     
         13 . The composition according to  claim 1  additionally containing: 
 UV-light absorbers and/or hindered amine light stabilizers,    flow control agents, and/or    degassing agents.    
     
     
         14 . A clear lacquer containing the thermosetting powder composition of  claim 1 .  
     
     
         15 . The thermosetting powder coating composition according to  claim 1  additionally containing at least one of pigments, dyes and fillers.  
     
     
         16 . A method for applying the thermosetting powder composition of  claim 1  which comprises applying it by an electrostatic or friction charging spray gun or fluidized bed technique.  
     
     
         17 . An entirely or partially coated substrate, wherein the coating material used, is a powder coating composition containing the composition according to  claim 1.